WASHINGTON — After a decade of negotiations among a dozen nations, the trade deal known as the Trans-Pacific Partnership, or T.P.P., is almost complete and ready for final consideration by Congress. But before President Obama can present the final document for approval, Congress must vote to give him the right to limit consideration of the T.P.P. to a single up-or-down vote, with no filibusters or amendments allowed. That is called trade promotion authority, or T.P.A., and, so far, Mr. Obama has failed to get it.

Q.What is the T.P.P., and who wants it?

A. The T.P.P. is a 30-chapter document that promises to ease trade restrictions among the United States and 11 Pacific Rim nations, which together represent an annual gross domestic product of nearly $28 trillion, or 40 percent of the world’s G.D.P. It is being pushed by Mr. Obama, many Republicans and a handful of Democrats on behalf of American businesses, who say it will open lucrative new markets. Critics, including most Democrats, say it is a giveaway to big business that will encourage companies to shift manufacturing jobs to low-wage nations.

Q.Why doesn’t Congress just vote on the T.P.P. when it is finished?

A. After years of mostly secret talks among the United States and other nations, the deal would unravel if United States lawmakers had the right to amend it. So backers are pushing to give the president T.P.A. — the ability to present the agreement as a take-it-or-leave-it decision. Lawmakers could not filibuster or amend the deal, but they could reject it. That is the way previous trade deals, including the North American Free Trade Agreement, or Nafta, were approved in Congress. If Mr. Obama doesn’t get T.P.A., he is certain to leave office without the trade deal he says is critical to the American economy’s long-term health.

Q. Didn’t the Senate already pass a bill giving T.P.A. to Mr. Obama?

A. Yes. In late May, a bipartisan coalition that included most of the Republicans and 14 Democrats agreed by a vote of 62-37 to give the president trade promotion authority for up to six years. But they did so only after reaching a deal with Democrats to include more money for trade adjustment assistance, or T.A.A., a program designed to help American workers displaced by global trade. That program is beloved by Democrats and hated by Republicans, who call it a waste of money designed largely to benefit labor unions. The legislation passed by the Senate packaged T.P.A. and T.A.A. together in a bid to win support from both parties — and it worked.

Q. So did the House take up the same package?

A. In the House, Speaker John A. Boehner chose to have lawmakers vote on the two parts of the Senate package — T.A.A. and T.P.A. — separately. He was betting that Democrats would ensure that the trade-assistance measure would pass, and that enough Republicans would back the T.P.A. so that it passed, too. Once both were approved in the House, Mr. Boehner thought, the package would go to Mr. Obama for his signature. And that would clear the way for final consideration of the trade deal.

Q. But it didn’t work out that way. What happened?

A. Democrats in the House who oppose the trade deal realized that they might not be able to defeat the authority part of the package. So instead, they decided to sacrifice the part of the Senate package that they liked — the trade assistance for workers — in a bid to halt the legislative progress. By voting en masse against the assistance measure (along with many Republicans, who oppose the program anyway), Democrats killed that part of the trade package. Even though the other part — the T.P.A. — narrowly passed, the package cannot be passed to Mr. Obama because it is different from what passed in the Senate.

Q.So what happens now?

A. That’s unclear. If the House could pass the trade-assistance part of the package, it could go to Mr. Obama for his signature. But there appears to be little support among Republicans in the House to pass a measure they dislike, and Democrats are refusing to budge. On Tuesday, Mr. Boehner pushed through an extension that allows members to consider the issue for another six weeks. That could allow Mr. Obama and his supporters to try to reach a deal in which Democrats drop their opposition to the trade assistance in exchange for getting something else they want. That could include promises of protections for workers or it could include unrelated measures, like passage of a long-stalled transportation bill.

Q. It’s so confusing, especially with so many similar-sounding abbreviations. Why couldn’t this all be simpler?

A. Very true. But perhaps Washington politicians are just adapting to the Internet slang common among young people. In 140 characters: Mr. Obama really wants to get T.P.P., but he needs T.P.A. and that requires T.A.A. Democrats like T.A.A. but will kill it to block T.P.A. #LOL

A version of this article appears in print on , on Page A18 of the New York edition with the headline: Issues and Obstacles in a Pacific Trade Deal. Order Reprints | Today’s Paper | Subscribe